Developments in semiconductor devices are accompanied by increasingly higher degrees of element integration, resulting in increased miniaturization of each element and a reduction in operating voltage. For example, in the field of MONOS (metal oxide nitride oxide semiconductor)-type non-volatile semiconductor devices which include a blocking film that separates a charge retaining layer and a gate electrode with the miniaturization of elements, the miniaturization of elements has led to demands for higher permittivity in blocking films Similarly, in the field of FG (floating gate)-type non-volatile semiconductor devices, the miniaturization of elements has led to demands for higher permittivity in insulating films between a floating electrode and a gate electrode. Furthermore, in the field of advanced CMOS device development, techniques for reducing gate leakage current by increasing the physical thickness of a gate insulating film using high permittivity material are being considered. Moreover, it is required that high dielectric films are heat-resistant with respect to a 1000° C.-annealing treatment performed during the manufacturing process of the semiconductor devices described above. Furthermore, it is required that the surfaces of high dielectric films have superior flatness for the purpose of suppressing variations in the operating voltages of the semiconductor devices.
As means for increasing the relative permittivity of a dielectric film, the use of HfO2, ZrO2, and Al2O3 as dielectric films having a higher relative permittivity than conventional SiO2 film, SiN film, or SiON film combining the two, is being considered. In addition, more recently, research is being performed on dielectric films in which a metallic element is doped on a laminated (stacked) structure made of HfO2, ZrO2, or Al2O3 or on HfO2 or ZrO2 for the purpose of suppressing leakage current associated with thinner dielectric films.
Methods of forming a high dielectric film include a CVD (chemical vapor deposition) method, an atomic layer adsorption/deposition method, and a sputtering method. A CVD method involves an incubation time during the formation process and is therefore problematic with respect to film thickness controllability, in-plane uniformity, and reproducibility. On the other hand, with a sputtering method, an interfacial layer is problematically formed due to plasma damage or oxidation of a processed substrate.
As a technique of forming a high-permittivity dielectric film by an ALD method or a CVD method, Patent Document 1 discloses a noncrystalline film made of AlxM(1−x)Oy (where M is a metal such as Hf and Zr capable of forming a crystalline dielectric) having a composition expressed as 0.05<x<0.3 in which noncrystalline aluminum oxide is contained in a crystalline dielectric. A feature of the technique is that a high relative permittivity ranging from 25 to 28 can be obtained with noncrystalline zircon aluminate. In addition, a relative permittivity of ZrO2 of 30 is described in Patent Document 1.
In addition, as a method of forming a high-permittivity dielectric film by sputtering, Patent Document 2 discloses a technique of forming ZrO2 by a sputtering method utilizing electron cyclotron resonance in a range where a stoichiometric composition is attained and in an oxygen supply range where the rate of decrease in sputtering rate arising from target surface oxidation reaches maximum.
Furthermore, Patent Document 3 describes a dielectric film in which ceramic targets of HfO2 and Y2O3 are used as sputtering targets and HfO2 is doped with yttrium (Y) as a metallic element and with nitrogen. According to Patent Document 3, it is described that by adding an element with a large atomic radius such as Y described above to monoclinic HfO2, aggregated energy of the cubical crystals decreases and stabilizes, and consequently, the crystalline system of HfO2 changes from monoclinic to tetragonal and then to cubical. As a result, it is described that a high dielectric film made of HfYO with a relative permittivity of 70 can be obtained. In addition, as oxygen in the monoclinic HfO2 is progressively replaced with nitrogen, the crystalline system changes from monoclinic to tetragonal, to rhombohedral, and then to cubical as the amount of nitrogen increases.
Patent Document 4 describes that with respect to a dielectric film made of ZrxSi(1−x)O(2−y) (0.81≦x≦0.99, 0.04≦x≦0.25), a dielectric film having tetragonal crystals is formed using Zr and Si targets by forming an amorphous film using a sputtering method in a mixed atmosphere of argon and oxygen and subsequently performing an annealing treatment at 750° C. or higher on the amorphous film in an atmosphere containing oxygen.
Non-Patent Document 1describes a dielectric film in which TiN is laminated (stacked) on the surface of HfO2 formed by an RF sputtering method. According to Non-Patent Document 1, it is described that when crystallization is performed in a state where TiN is laminated on HfO2, HfO2 having a cubic crystalline phase is formed and a dielectric film having a relative permittivity value of 50 is obtained.
Patent Documents
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-214304
Patent Document 2: Japanese Patent No. 3748218
Patent Document 3: Japanese Patent No. 3981094
Patent Document 4: Japanese Patent Application Laid-Open No. 2007-299878
Non-Patent Documents
Non-Patent Document 1: Symposium on VLSI Technology Digest of Technical Papers, 2008, p. 152.